In continuous casting, liquid metal is poured into the upper end of the vertically throughgoing cavity of a mold that is cooled so that before the metal reaches the lower end of the cavity at least the outer portions of the liquid-metal mass are hard enough to form a coherent shape that is pulled from the mold as a continuous strand. When steel strip is being formed the mold has two broad side walls bridged at their ends by two narrow walls. Granular additives are added at the top of the mold to form a protective and lubricating slag.
In order to make the faces of the strip as smooth as possible it has been suggested in European patent application No. 1,149,734 and in my earlier U.S. Pat. No. 4,721,151 to flare the mold cavity at an upper central region where the liquid metal is introduced into the mold, that is shape the cavity in this region so its flow cross section decreases downward. In the center of the top of the cavity the inside surfaces of the broad side walls of the mold are cut back to achieve this effect. End regions of these inner surfaces are parallel to each other so that the tapering only actually exists at the upper region of the mold cavity in its center.
Such a system somewhat reduces surface imperfections in the steel strip produced, but still leaves a substantial number of flaws, particularly near the edges of the strip. The improvement is evidently caused by entraining a small amount of the slag from atop the melt down along the sides of the mold. The resultant lubrication substantially eliminates wavy marks on the faces of the steel strip thus produced.